The present invention relates to a catalytic converter for the exhaust system of a motor vehicle.
The use of a catalytic converter in the exhaust system of motor vehicle is well known. The catalytic converter acts on the exhaust gases leaving the engine of the vehicle to convert carbon monoxide, the oxides of nitrogen, and hydrocarbons in the exhaust gases. A typical catalytic converter consists of a number of bricks (coated substrates) through which the exhaust gases can pass. In order to work efficiently, these bricks must be at a temperature which is above the light-off temperaturexe2x80x94the temperature above which conversion is most effectively achieved. The temperature of the exhaust gases is used to maintain the temperature of these bricks above the light-off temperature (the threshold temperature above which the catalyst is active). However, when the engine is started from cold, there is an initial period (the cold phase or light off time) when the catalytic converter is cold and inactive but exhaust gases are passing through the converter. During this initial period, the converter is not working in an efficient manner.
It is an object of the present invention to provide a catalytic converter with a reduced inactive period after a cold start.
A catalytic converter in accordance with the present invention for an exhaust system of a motor vehicle comprises a housing having an inlet and an outlet; a first brick positioned inside the housing adjacent the inlet for initiating catalytic light-off functions of exhaust gases flowing through the first brick; a second brick positioned adjacent the first brick downstream of the inlet for three way conversion of exhaust gases flowing through the second brick; a third brick positioned adjacent the second brick downstream of the inlet for hydrocarbon adsorption and oxidation of exhaust gases flowing through the third brick; and a fourth brick positioned adjacent and spaced from the third brick downstream of the inlet for light-off of exhaust gases flowing through the fourth brick; wherein the third brick is substantially annular with a through bore extending axially therethrough; and wherein the second brick has a closed bore extending axially and opening into the through bore of the third brick.
The catalytic converter of the present invention is such that the fourth brick is heated by exhaust gases passing through the aligned bores to its light-off temperature before the third brick reaches its threshold (desorption) temperature. Such an arrangement reduces the inactive period for the converter when compared to previously known arrangements with minimal increase in cost or complexity. In a preferred arrangement, the fourth brick is a coated metallic foam which enhances gas mixing in the brick and improves radial heat conduction.